Municipal and industrial wastewater treatment facilities often include primary, secondary and tertiary processes to treat wastewater to remove contaminants, such as suspended solids, biodegradable organics, phosphorus, nitrogen, microbiological contaminants, and the like, to provide a clean effluent. The clean effluent is typically subject to strict local, state and federal regulations.
The primary treatment processes often includes screens, grit chambers and/or primary clarifiers to remove large solids and other suspended matter to provide a primary effluent. Activated sludge is one type of secondary process which utilizes a biological reactor(s) which contains a large population of microorganisms that ingest contaminants in the primary effluent to form biological “flocs.” Oxygen is typically fed into the biological reactor(s) to promote growth of these biological flocs. The combination of primary effluent, or in some cases raw sewage, and biological flocs, is commonly known as mixed liquor. The population or concentration of microorganisms in the mixed liquor is often referred to as mixed liquor suspended solids (MLSS).
After sufficient treatment in the biological reactor, the biological flocs in the mixed liquor are then typically sent to a secondary clarifier where the biological flocs are separated by gravity from the mixed liquor to provide a secondary effluent and a settled sludge. The secondary effluent, or “clean” effluent, may be discharged back to the environment or processed by additional tertiary treatment processes. The majority of the settled sludge in the secondary clarifier is typically recycled back to the biological reactor by a return activated sludge subsystem. The remaining, excess sludge is wasted from the system to control the concentration of mixed liquor suspended solids.
However, separation of the biological flocs from the mixed liquor in the secondary clarifier is difficult because the biological flocs are only marginally heavier than water, and therefore settle slowly. As a result, the secondary clarifier of a typical activated sludge process is often the bottleneck in most wastewater treatment processes that utilize activated sludge as a secondary process. The crucial solids separation step of the biological flocs from the mixed liquor in the secondary clarifier is therefore typically the rate limiting process which is governed by a variety of factors, most notably the specific gravity, or density, of the biological flocs.
Moreover, solids separation in the secondary clarifier in a typical activated sludge processes may be unreliable due to the many types of settling problems that are caused by inter alia: overgrowth of filamentous organisms, viscous bulking caused by the overgrowth of either zoogleal organisms or exocellular polysaccharide material, pin floc, straggler floc, excessive solids loading on the secondary clarifiers, excessive secondary clarifier surface overflow rate, and the like.
Sequencing batch reactor (SBR) systems may also be used to treat wastewater. A typical conventional SBR system includes one or more sequencing batch reactors which contains a large population of microorganisms that ingest contaminants in the influent wastewater to form biological flocs and treat the wastewater. However, during the settling phase of a typical conventional SBR system, the biological flocs settle slowly because they are only marginally heavier than water. The solids separation in the settling phase is also unreliable due to the many types of settling problems discussed above. This can result in reduced treatment capacity and/or compromised effective quality.
Another method of treating wastewater, such as wastewater from breweries, pharmaceutical plants, food processing plants, pulp and paper facilities, ethanol production facilities, and the like, is to use an anaerobic treatment reactor. The anaerobic treatment reactor creates an anaerobic environment which contains a population of microorganisms that ingest contaminants in the influent wastewater to form biological flocs and treat the wastewater. The wastewater is typically fed near the bottom of the anaerobic treatment reactor and into a sludge blanket where the microorganisms consume the waste therein. In operation, wastewater fed into the bottom of the anaerobic treatment reactor flows upward through the anaerobic sludge blanket to treat the wastewater.
However, if the flow rate of influent wastewater is too fast, the anaerobic sludge blanket can expand and become diffuse. The result may be an excess loss of microorganisms in the treated effluent which may compromise the quality of the treated effluent.